System and method for quantization of angles for beamforming feedback

ABSTRACT

An embodiment method for beamforming feedback includes receiving a sounding packet for a beamforming transmission, performing planar rotation in accordance with the sounding packet to generate phi and psi angle values, quantizing the phi and psi angle values to a same bit resolution, and feeding back the quantized phi and psi angle values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/243,714, filed on Aug. 22, 2016, now U.S. Pat. No. 9,887,749, whichclaims the benefit of U.S. Provisional Application No. 62/268,361, filedon Dec. 16, 2015, which applications are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a system and method for wirelesscommunications, and, in particular embodiments, to a system and methodfor quantization of angles for beamforming feedback.

BACKGROUND

Beamforming is a technique whereby a beamformer station directs a signaltoward a beamformee station rather than broadcasting the signal in asubstantially omnidirectional manner. A beamformer may be defined as astation that transmits a physical layer convergence procedure (PLCP)protocol data unit (PPDU) using a beamforming steering matrix. Abeamformee may be defined as a station that receives a PPDU that wastransmitted using a beamforming steering matrix. The beamformer stationmay be a component configured to provide wireless access to a network,such as an enhanced base station (eNB), a macrocell, a femtocell, aWi-Fi access point, or some other wirelessly enabled device. Any suchcomponent will be referred to herein as an access point. An access pointmay provide wireless access in accordance with one or more wirelesscommunication protocols, such as Long Term Evolution (LTE), LTE Advanced(LTE-A), High Speed Packet Access (HSPA), or Wi-Fi 802.11a/b/g/n/ac. Thebeamformee station may be a component capable of establishing a wirelessconnection with an access point, such as a user equipment (UE), a mobilestation, or some other wirelessly enabled device. Any such componentwill be referred to herein as a station. While beamforming is typicallyemployed in transmissions from access points to stations, it should beunderstood that a station may employ beamforming when transmitting to anaccess point. Further any station may simultaneously act as a beamformerand beamformee, while transmitting and receiving, respectively.

SUMMARY

An embodiment method for beamforming feedback includes receiving asounding packet for a beamforming transmission, performing planarrotation in accordance with the sounding packet to generate phi and psiangle values, quantizing the phi and psi angle values to a same bitresolution, and feeding back the quantized phi and psi angle values.

An embodiment station includes a processor and a non-transitory computerreadable storage medium storing programming for execution by theprocessor. The programming includes instructions for receiving asounding packet for a beamforming transmission, performing planarrotation in accordance with the sounding packet to generate phi and psiangle values, quantizing the phi and psi angle values to a same bitresolution, and feeding back the quantized phi and psi angle values.

An embodiment method for beamforming feedback includes transmitting asounding packet for a beamforming transmission, receiving feedbackincluding quantized phi and psi angle values having a same bitresolution, beamforming transmit channels in accordance with thequantized phi and psi angle values, and transmitting the beamformeddata.

An embodiment access point includes a processor and a non-transitorycomputer readable storage medium storing programming for execution bythe processor. The programming includes instructions for transmitting asounding packet for a beamforming transmission, receiving feedbackincluding quantized phi and psi angle values having a same bitresolution, beamforming transmit channels in accordance with thequantized phi and psi angle values, and transmitting the beamformeddata.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 is an angular representation of Givens rotation parameters;

FIG. 2 is an angular representation of Givens rotation parameters basedon a disclosed embodiment;

FIG. 3 illustrates simulation results for single user beamforming;

FIG. 4 illustrates simulation results for multiple user beamforming;

FIG. 5 is a flowchart of an embodiment method for beamforming feedback;

FIG. 6 is a flowchart of an alternative embodiment method forbeamforming feedback;

FIG. 7 illustrates a block diagram of an embodiment processing systemfor performing methods described herein; and

FIG. 8 illustrates a block diagram of a transceiver adapted to transmitand receive signaling over a telecommunications network.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The structure, manufacture and use of the presently preferredembodiments are discussed in detail below. It should be appreciated,however, that the present invention provides many applicable inventiveconcepts that can be embodied in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to make and use the invention, and do not limit the scope of theinvention.

Beamforming is described in the Institute of Electrical and ElectronicsEngineers (IEEE) standards 802.11ac-2013 and 802.11n-2009, both of whichare incorporated herein by reference in their entireties. Beamformingis, according to that standard, preceded by channel sounding.Specifically, the beamformer begins the process by transmitting a NullData Packet (NDP) Announcement frame, which is used to gain control ofthe channel and identify beamformees. The beamformer follows the NDPAnnouncement with a null data packet. The receiver may analyze theOrthogonal Frequency Division Multiplexing (OFDM) training fields in thenull data packet to calculate the channel response. For multi-usertransmissions, multiple NDPs may be transmitted. A beamformee mayanalyze the training fields in the received NDP and calculate a feedbackmatrix. The feedback matrix is referred to by the letter V in the802.11ac specification. The beamformer receives the feedback matrix andcalculates a steering matrix to direct transmissions toward thebeamformee.

The information generated by the analysis of the channel conditionsbetween the beamformee and the beamformer may take the form of a rightsingular matrix known as V. V may be highly complex and thus unsuitablefor transmission in its raw form. To make the channel conditioninformation more suitable for transmission, V may be transformed by aprocedure known as a Givens rotation, which produces two angles known asphi (Φ) and psi (Ψ). The beamformee quantizes the angles phi and psi andfeeds the quantized angles back to the beamformer. The beamformer usesphi and psi to reconstruct V and thereby learns the channel steeringconditions between itself and the beamformee. The beamformer then usesthe channel steering condition information to shape a beam for atransmission to the beamformee.

More specifically, the 802.11ac/n standards use Givens rotations toperform a planar rotation operation on a unitary matrix V. The operationresults in the generation of the angles Φ and Ψ. After being convertedto polar coordinates, the angles are quantized. The angles Φ arequantized between 0 and 2π and the angles Ψ are quantized between 0 andπ/2, as given by:

${\Phi = {\frac{k\;\pi}{2^{b_{\phi} - 1}} + \frac{\pi}{2^{b_{\phi}}}}},$where k=0, 1, . . . , 2^(b) ^(ϕ) −1 and b_(ϕ) is the number of bits toquantize Φ

${\Psi = {\frac{k\;\pi}{2^{b_{\psi} + 1}} + \frac{\pi}{2^{b_{\psi} + 2}}}},$where k=0, 1, . . . 2^(b) ^(Ψ) −1 and b_(Ψ) is the number of bits toquantize Ψ

The quantization bit resolutions per tone for phi and psi have a two bitdifference with respect to each other in 802.11ac/n to keep the samemean square quantization error for both phi and psi. More specifically,the 802.11ac/n standards call for the number of bits for phi to be twogreater than the number of bits for psi. The specific number of bitsused for each angle depends on whether single user multiple-inputmultiple-output (SU-MIMO) or multiple user-MIMO (MU-MIMO) is employed.For example, there may be four bits per tone for phi and two bits pertone for psi in the case of SU-MIMO and seven bits per tone for phi andfive bits per tone for psi in the case of MU-MIMO.

FIG. 1 illustrates angular representations of Givens rotation parameterswhere the number of bits for phi (b_(ϕ))=₅ and the number of bits forpsi (b_(Ψ))=3. Since five bits are used for phi, 2⁵ or 32 values arepossible for phi. Since three bits are used for psi, 2³ or 8 values arepossible for psi. That is, four times as many values are possible forphi as for psi. Phi is quantized between 0 and 2π, or a rotation throughan entire circle no. Psi is quantized between 0 and π/2, or a rotationthrough one quadrant 120 of a circle. Thus, with four times as manyvalues for phi as for psi, and with phi quantized through a rotationfour times as large as that for psi, the span between angles is the samefor phi and psi. In other words, the same quantization steps are usedfor phi and psi, and therefore the granularity is the same for phi andpsi, and the quantized resolutions are the same, in radians, for the twoangle parameters. In this simplified representation of the proportionalresolutions for the Givens rotations used to perform planar rotationoperations, the values 5 and 3 were used for b_(ϕ) and b_(Ψ),respectively. Other values may be used in 802.11n and 802.11ac wirelessnetworks, but the relationship b_(ϕ)=b_(Ψ)+2 is preserved in thosestandards.

The 802.11n and 802.11ac standards provide that the number of bits forphi and the number of bits for psi are to be specified in the CodebookInformation subfield of the very high throughput (VHT) MIMO Controlfield in a beamforming action frame transmitted by a station. When theCodebook Information subfield is set to 0, two bits are used for psi andfour bits are used for phi in the case of SU-MIMO. In the case ofMU-MIMO, when the Codebook Information subfield is set to 0, five bitsare used for psi and seven bits are used for phi. When the CodebookInformation subfield is set to 1, four bits are used for psi and sixbits are used for phi in the case of SU-MIMO. In the case of MU-MIMO,when the Codebook Information subfield is set to 1, seven bits are usedfor psi and nine bits are used for phi.

In the existing 802.11n and 802.11ac standards, the quantizedresolutions, in radians, for both phi and psi are the same since twomore bits are always used for phi than for psi. However, psi generallyis more important than phi in Givens rotations. The series of Givensrotations below are an example of a representation of the V matrix.

$\begin{bmatrix}1 & 0 & 0 & 0 \\0 & {\cos\left( \psi_{4,2} \right)} & 0 & {\sin\left( \psi_{4,2} \right)} \\0 & 0 & 1 & 0 \\0 & {- {\sin\left( \psi_{4,2} \right)}} & 0 & {\cos\left( \psi_{4,2} \right)}\end{bmatrix}{\quad{\begin{bmatrix}1 & 0 & 0 & 0 \\0 & {\cos\left( \psi_{3,2} \right)} & {\sin\left( \psi_{3,2} \right)} & 0 \\0 & {- {\sin\left( \psi_{3,2} \right)}} & {\cos\left( \psi_{3,2} \right)} & 0 \\0 & 0 & 0 & 1\end{bmatrix}{\quad{\quad{\quad{\begin{bmatrix}1 & 0 & 0 & 0 \\0 & e^{j\;\phi_{2,2}} & 0 & 0 \\0 & 0 & e^{j\;\phi_{2,2}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}^{*}{\quad{{\begin{bmatrix}{\cos\left( \psi_{4,1} \right)} & 0 & 0 & {\sin\left( \psi_{4,1} \right)} \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\{- {\sin\left( \psi_{4,1} \right)}} & 0 & 0 & {\cos\left( \psi_{4,1} \right)}\end{bmatrix}\begin{bmatrix}{\cos\left( \psi_{3,1} \right)} & 0 & {\sin\left( \psi_{3,1} \right)} & 0 \\0 & 1 & 0 & 0 \\{- {\sin\left( \psi_{3,1} \right)}} & 0 & {\cos\left( {{\psi 3},1} \right)} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}{\quad{{{\begin{bmatrix}{\cos\left( \psi_{2,1} \right)} & {\sin\left( \psi_{2,1} \right)} & 0 & 0 \\{- {\sin\left( \psi_{2,1} \right)}} & {\cos\left( \psi_{2,1} \right)} & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}\begin{bmatrix}e^{j\;\phi_{1,1}} & 0 & 0 & 0 \\0 & e^{j\;\phi_{2,2}} & 0 & 0 \\0 & 0 & e^{j\;\phi_{3,3}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}^{*}{V\begin{bmatrix}e^{j\;\theta_{1}} & 0 \\0 & e^{j\;\theta_{2}}\end{bmatrix}}^{*}} = \begin{bmatrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{bmatrix}}}}}}}}}}}$

It can be seen that the psi angles in the Givens rotations are used morefrequently than the phi angles. More specifically, psi appears in fiveof the seven 4×4 matrices, but phi appears in only two of the seven 4×4matrices. Furthermore, in the matrices in which phi appears, phi affectsonly the diagonal elements. Therefore, phi may be considered lessimportant than psi in Givens rotations. Thus, the difference of two bitsbetween phi and psi may not be necessary, and an equal bit resolutionfor both phi and psi may be acceptable for performing beamformingfeedback. That is, feedback overhead may be reduced at small cost ofperformance degradation by selecting a non-proportional quantization,i.e., b_(ϕ)≈b_(Ψ)+2.

An embodiment uses two fewer bits for quantizing the angle phi comparedto the number of bits for quantizing phi specified in the 802.11standards. In particular, in an embodiment, b_(ϕ)=b_(Ψ), where b_(ϕ) ismade equal to b_(Ψ) by reducing b, by two bits. That is, an embodimentprovides equal bit resolution for the angles in beamformingquantization. For example, in the case of SU-MIMO, two bits per tone maybe used for both phi and psi, instead of four for phi and two for psi ascurrently specified in the 802.11 standards. Similarly, in the case ofMU-MIMO, five bits per tone may be used for both phi and psi, instead ofseven for phi and five for psi as currently specified in the 802.11standards. In this way, the quantization overhead in the feedback ofchannel condition information for beamforming may be reduced.

In an embodiment, the meanings of the values in the Codebook Informationsubfield of the VHT MIMO Control field in a beamforming action frametransmitted by a station differ from the meanings specified in thecurrent 802.11 standards. For example, in the case of single userfeedback, a 0 in the Codebook Information subfield may indicate that twobits are used for both phi and psi, and a 1 in the Codebook Informationsubfield may indicate that four bits are used for both phi and psi. Inthe case of multiple user feedback, a 0 in the Codebook Informationsubfield may indicate that five bits are used for both phi and psi, anda 1 in the Codebook Information subfield may indicate that seven bitsare used for both phi and psi. In other embodiments, the values of 0 and1 in the Codebook Information subfield may indicate other numbers ofbits, but in any case the number of bits is the same for phi and psi.The names of the Codebook Information subfield and the VHT MIMO Controlfield may differ in future 802.11 amendments, but the above binaryvalues may apply to any equivalent fields.

In an embodiment, a subfield, which may be referred to as the AdditionalQuantization subfield, is added to the Per User Info field of the nulldata packet announcement (NDPA) transmitted by a beamformer as asounding packet for use by a beamformee in analyzing channel conditions.A beamformer may set the Additional Quantization subfield to either 2 or3 to indicate the number of bits to be used by a beamformee for phi andpsi in SU-MIMO and MU-MIMO. In an embodiment, when the AdditionalQuantization subfield is set to 2, two bits to be are used for both phiand psi in the case of SU-MIMO. In the case of MU-MIMO, when theAdditional Quantization subfield is set to 2, five bits are to be usedfor both phi and psi. When the Additional Quantization subfield is setto 3, four bits are to be used for both phi and psi in the case ofSU-MIMO. In the case of MU-MIMO, when the Additional Quantizationsubfield is set to 3, seven bits are to be used for both phi and psi. Inother embodiments, other values may be used in the AdditionalQuantization subfield, and the values in the Additional Quantizationsubfield may indicate that other numbers of bits are to be used for bothphi and psi.

FIG. 2 is an embodiment angular representation of Givens rotationparameters used to perform planar rotation operations, based on thedisclosed idea of equal bit allocation for both phi and psi, whereb_(ϕ)=₃ and b_(Ψ)=3. Since b_(ϕ)=b_(Ψ) and the angle span of phi is fourtimes the angle span of psi, the quantized resolution of phi is ¼ thatof psi. That is, since three bits are used for both phi and psi, 2³ or 8values are possible for both phi and psi. Phi is again quantized between0 and 2π or a rotation through an entire circle 210, and psi is againquantized between 0 and π/2 or a rotation through one quadrant 220 of acircle. Thus, with an equal number of values for phi and for psi, andwith phi quantized through a rotation four times as large as that forpsi, the span between angles for phi is four times greater than that forpsi. In other words, different quantization steps are used for phi andpsi in this embodiment, and therefore the granularity is different forphi and psi. In particular, the granularity for phi is reduced comparedto the granularity for psi, and the quantized resolutions are differentfor the two angle parameters. Other values may be used for b_(ϕ) andb_(Ψ) in other embodiments, but the relationship b_(ϕ)=b_(Ψ) ispreserved in the embodiments.

Simulations were performed to compare the 4/2 bits per anglequantization specified in the 802.11 standards for single userbeamforming to the embodiment 2/2 bits per angle quantization for singleuser beamforming. A single beamformer was used with one spatial streamand four transmission antennas. The beamformee had two receive antennas.Further simulation parameters included a Task Group n with a channel Dmodel (TGnD), non-line-of-sight (NLOS), minimum mean square error (MMSE)interference cancellation detection, quadrature phase shift keying(QPSK) with rate 1/2 binary convolutional coding (BCC) with a ViterbiDecoder, and measurement of the packet error rate (PER) with a packetsize of 200 bytes. In the simulations, very minimal performancedegradation was observed with the embodiment equal bit resolution forboth phi and psi. FIG. 3 illustrates simulation results 300 for singleuser beamforming. It can be seen that, when the 802.11-based 4 bits forphi/2 bits for psi case 310 is compared to the embodiment 2 bits forphi/2 bits for psi case 320, there is only a 0.3 decibel (dB)performance degradation in the 2 bits for phi/2 bits for psi case 320,while feedback overhead is reduced by 33%.

Additional simulations were performed to compare the 7/5 bits per anglequantization specified in the 802.11 standards for multi-userbeamforming to the embodiment 5/5 bits per angle quantization formulti-user beamforming. A single beamformer was used with one spatialstream per station and four transmission antennas. Two beamformees wereused with two receive antennas per station. Further simulationparameters included TGnD NLOS, MMSE detection, QPSK with rate 1/2 BCCwith a Viterbi Decoder, and PER with a packet size of 200 bytes. FIG. 4illustrates simulation results 400 for multi-user beamforming. It can beseen that, when the 802.11-based 7 bits for phi/5 bits for psi case 410is compared to the embodiment 5 bits for phi/5 bits for psi case 420,overhead is reduced by 17% with almost no degradation in the 5 bits forphi/5 bits for psi case 420.

FIG. 5 is a flowchart of an embodiment method 500 for beamformingfeedback. At block 510, a sounding packet for a beamforming transmissionis received. At block 520, a planar rotation is performed in accordancewith the sounding packet to generate phi and psi angle values. At block530, the phi and psi angle values are quantized to the same bitresolution. At block 540, the quantized phi and psi angle values are fedback.

FIG. 6 is a flowchart of an alternative embodiment method 600 forbeamforming feedback. At block 610, a sounding packet for a beamformingtransmission is transmitted. At block 620, feedback including quantizedphi and psi angle values having the same bit resolution is received. Atblock 630, transmit channels are beamformed in accordance with thequantized phi and psi angle values. At block 640, the beamformedtransmit channels are transmitted.

FIG. 7 illustrates a block diagram of an embodiment processing system700 for performing methods described herein, which may be installed in ahost device such as a WLAN beamformer or beamformee. As shown, theprocessing system 700 includes a processor 704, a memory 706, andinterfaces 710-614, which may (or may not) be arranged as shown in thefigure. The processor 704 may be any component or collection ofcomponents adapted to perform computations and/or other processingrelated tasks, and the memory 706 may be any component or collection ofcomponents adapted to store programming and/or instructions forexecution by the processor 704. In an embodiment, the memory 706includes a non-transitory computer readable medium. The interfaces 710,712, 714 may be any component or collection of components that allow theprocessing system 700 to communicate with other devices/componentsand/or a user. For example, one or more of the interfaces 710, 712, 714may be adapted to communicate data, control, or management messages fromthe processor 704 to applications installed on the host device and/or aremote device. As another example, one or more of the interfaces 710,712, 714 may be adapted to allow a user or user device (e.g., personalcomputer (PC), etc.) to interact/communicate with the processing system700. The processing system 700 may include additional components notdepicted in the figure, such as long term storage (e.g., non-volatilememory, etc.).

In some embodiments, the processing system 700 is included in a networkdevice that is accessing, or part otherwise of, a telecommunicationsnetwork. In one example, the processing system 700 is in a network-sidedevice in a wireless or wireline telecommunications network, such as abase station, a relay station, a scheduler, a controller, a gateway, arouter, an applications server, or any other device in thetelecommunications network. In other embodiments, the processing system700 is in a user-side device accessing a wireless or wirelinetelecommunications network, such as a mobile station, a user equipment(UE), a personal computer (PC), a tablet, a wearable communicationsdevice (e.g., a smartwatch, etc.), or any other device adapted to accessa telecommunications network.

In some embodiments, one or more of the interfaces 710, 712, 714connects the processing system 700 to a transceiver adapted to transmitand receive signaling over the telecommunications network. FIG. 8illustrates a block diagram of a transceiver 800 adapted to transmit andreceive signaling over a telecommunications network. The transceiver 800may be installed in a host device. As shown, the transceiver 800comprises a network-side interface 802, a coupler 804, a transmitter806, a receiver 808, a signal processor 810, and a device-side interface812. The network-side interface 802 may include any component orcollection of components adapted to transmit or receive signaling over awireless or wireline telecommunications network. The coupler 804 mayinclude any component or collection of components adapted to facilitatebi-directional communication over the network-side interface 802. Thetransmitter 806 may include any component or collection of components(e.g., up-converter, power amplifier, etc.) adapted to convert abaseband signal into a modulated carrier signal suitable fortransmission over the network-side interface 802. The receiver 808 mayinclude any component or collection of components (e.g., down-converter,low noise amplifier, etc.) adapted to convert a carrier signal receivedover the network-side interface 802 into a baseband signal. The signalprocessor 810 may include any component or collection of componentsadapted to convert a baseband signal into a data signal suitable forcommunication over the device-side interface(s) 812, or vice-versa. Thedevice-side interface(s) 812 may include any component or collection ofcomponents adapted to communicate data-signals between the signalprocessor 810 and components within the host device (e.g., theprocessing system 700, local area network (LAN) ports, etc.).

The transceiver 800 may transmit and receive signaling over any type ofcommunications medium. In some embodiments, the transceiver 800transmits and receives signaling over a wireless medium. For example,the transceiver 800 may be a wireless transceiver adapted to communicatein accordance with a wireless telecommunications protocol, such as acellular protocol (e.g., long-term evolution (LTE), etc.), a wirelesslocal area network (WLAN) protocol (e.g., Wi-Fi, etc.), or any othertype of wireless protocol (e.g., Bluetooth, near field communication(NFC), etc.). In such embodiments, the network-side interface 802comprises one or more antenna/radiating elements. For example, thenetwork-side interface 802 may include a single antenna, multipleseparate antennas, or a multi-antenna array configured for multi-layercommunication, e.g., single input multiple output (SIMO), multiple inputsingle output (MISO), multiple input multiple output (MIMO), etc. Inother embodiments, the transceiver 800 transmits and receives signalingover a wireline medium, e.g., twisted-pair cable, coaxial cable, opticalfiber, etc. Specific processing systems and/or transceivers may utilizeall of the components shown, or only a subset of the components, andlevels of integration may vary from device to device.

It should be appreciated that one or more steps of the embodimentmethods provided herein may be performed by corresponding units ormodules. For example, a signal may be transmitted by a transmitting unitor a transmitting module. A signal may be received by a receiving unitor a receiving module. A signal may be processed by a processing unit ora processing module. Other steps may be performed by a performingunit/module, a quantizing unit/module, a feedback unit/module, a settingunit/module, and/or a beamforming unit/module. The respectiveunits/modules may be hardware, software, or a combination thereof. Forinstance, one or more of the units/modules may be an integrated circuit,such as field programmable gate arrays (FPGAs) or application-specificintegrated circuits (ASICs).

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method for beamforming feedback comprising:receiving a sounding packet for a beamforming transmission; performingplanar rotation in accordance with the sounding packet to generate phiand psi angle values; quantizing the phi and psi angle values such thata quantized resolution of the phi angle value is different from aquantized resolution of the psi angle value; and feeding back thequantized phi and psi angle values.
 2. The method of claim 1, whereinthe planar rotation is a Givens rotation.
 3. The method of claim 1,wherein quantizing the phi and psi angle values comprises using a firstnumber of bits for quantizing phi that has been set to be equal to asecond number of bits for quantizing psi.
 4. The method of claim 1,further comprising, in a case of single user feedback, setting aCodebook Information subfield of a very high throughput (VHT)multiple-input multiple-output (MIMO) Control field specified in anInstitute of Electrical and Electronics Engineers (IEEE) 802.11 standardto 0 to indicate that a first number of bits are used for both phi andpsi, and setting the Codebook Information subfield to 1 to indicate thata second number of bits are used for both phi and psi.
 5. The method ofclaim 4, further comprising, in a case of multiple user feedback,setting the Codebook Information subfield to 0 to indicate that a thirdnumber of bits are used for both phi and psi, and setting the CodebookInformation subfield to 1 to indicate that a fourth number of bits areused for both phi and psi.
 6. The method of claim 1, wherein thesounding packet is a null data packet announcement (NDPA) received froma beamformer, wherein the NDPA includes a subfield added to a Per UserInfo field, wherein, when the subfield is set to a first value, a firstnumber of bits are used for both phi and psi in a case of single user(SU)-MIMO and a second number of bits are used for both phi and psi in acase of multiple user (MU)-MIMO, and wherein, when the subfield is setto a second value, a third number of bits are used for both phi and psiin the case of SU-MIMO and a fourth number of bits are used for both phiand psi in the case of MU-MIMO.
 7. A station comprising: anon-transitory memory storage comprising instructions; and one or moreprocessors in communication with the memory, wherein the one or moreprocessors execute the instructions for: receiving a sounding packet fora beamforming transmission; performing planar rotation in accordancewith the sounding packet to generate phi and psi angle values;quantizing the phi and psi angle values such that a quantized resolutionof the phi angle value is different from a quantized resolution of thepsi angle value; and feeding back the quantized phi and psi anglevalues.
 8. The station of claim 7, wherein the planar rotation is aGivens rotation.
 9. The station of claim 7, wherein quantizing the phiand psi angle values comprises using a first number of bits forquantizing phi that has been set to be equal to a second number of bitsfor quantizing psi.
 10. The station of claim 7, further comprising theone or more processors executing the instructions for, in a case ofsingle user feedback, setting a Codebook Information subfield of a veryhigh throughput (VHT) multiple-input multiple-output (MIMO) Controlfield specified in an institute of Electrical and Electronics Engineers(IEEE) 802.11 standard to 0 to indicate that a first number of bits areused for both phi and psi, and setting the Codebook Information subfieldto 1 to indicate that a second number of bits are used for both phi andpsi.
 11. The station of claim 10, further comprising the one or moreprocessors executing the instructions for, in a case of multiple userfeedback, setting the Codebook Information subfield to 0 to indicatethat a third number of bits are used for both phi and psi, and settingthe Codebook Information subfield to 1 to indicate that a fourth numberof bits are used for both phi and psi.
 12. The station of claim 7,wherein the sounding packet is a null data packet announcement (NDPA)received from a beamformer, wherein the NDPA includes a subfield addedto a Per User Info field, wherein, when the subfield is set to a firstvalue, the one or more processors execute the instructions to use afirst number of bits for both phi and psi in a case of single user(SU)-MIMO and use a second number of bits for both phi and psi in a caseof multiple user (MU)-MIMO, and wherein, when the subfield is set to asecond value, the one or more processors execute the instructions to usea third number of bits for both phi and psi in the case of SU-MIMO anduse a fourth number of bits for both phi and psi in the case of MU-MIMO.13. A method for beamforming feedback comprising: transmitting asounding packet for a beamforming transmission; receiving feedbackincluding quantized phi and psi angle values, the quantized phi anglevalue being different from the quantized psi angle value; beamformingtransmit channels in accordance with the quantized phi and psi anglevalues; and transmitting the beamformed transmit channels.
 14. Themethod of claim 13, wherein the phi and psi angle values have beenquantized in accordance with a Givens rotation.
 15. The method of claim13, wherein a first number of bits for quantizing phi has been set to beequal to a second number of bits for quantizing psi.
 16. The method ofclaim 13, further comprising, in a case of single user feedback,processing a value of 0 in a Codebook Information subfield of a veryhigh throughput (VHT) multiple-input multiple-output (MIMO) Controlfield specified in an Institute of Electrical and Electronics Engineers(IEEE) 802.11 standard as an indication that a first number of bits areused for both phi and psi, and processing a value of 1 in the CodebookInformation subfield as an indication that a second number of bits areused for both phi and psi.
 17. The method of claim 16, furthercomprising, in a case of multiple user feedback, processing a value of 0in the Codebook Information subfield as an indication that a thirdnumber of bits are used for both phi and psi, and processing a value of1 in the Codebook Information subfield as an indication that a fourthnumber of bits are used for both phi and psi.
 18. The method of claim13, wherein the sounding packet is a null data packet announcement(NDPA), wherein the NDPA includes a subfield added to a Per User Infofield, wherein, when a first number of bits are to be used for both phiand psi in a case of single user (SU)-MIMO and a second number of bitsare to be used for both phi and psi in a case of multiple user(MU)-MIMO, the subfield is set to a first value, and wherein, when athird number of bits are to be used for both phi and psi in the case ofSU-MIMO and a fourth number of bits are to be used for both phi and psiin the case of MU-MIMO, the subfield is set to a second value.
 19. Anaccess point comprising: a non-transitory memory storage comprisinginstructions; and one or more processors in communication with thememory, wherein the one or more processors execute the instructions for:transmitting a sounding packet for a beamforming transmission; receivingfeedback including quantized phi and psi angle values, the quantized phiangle value being different from the quantized psi angle value;beamforming transmit channels in accordance with the quantized phi andpsi angle values; and transmitting the beamformed transmit channels. 20.The access point of claim 19, wherein the phi and psi angle values havebeen quantized in accordance with a Givens rotation.
 21. The accesspoint of claim 19, wherein a first number of bits for quantizing phi hasbeen set to be equal to a second number of bits for quantizing psi. 22.The access point of claim 19, further comprising the one or moreprocessors executing the instructions for, in a case of single userfeedback, processing a value of 0 in a Codebook Information subfield ofa very high throughput (VHT) multiple-input multiple-output (MIMO)Control field specified in an Institute of Electrical and ElectronicsEngineers (IEEE) 802.11 standard as an indication that a first number ofbits are used for both phi and psi, and processing a value of 1 in theCodebook Information subfield as an indication that a second number ofbits are used for both phi and psi.
 23. The access point of claim 22,further comprising the one or more processors executing the instructionsfor, in a case of multiple user feedback, processing a value of 0 in theCodebook Information subfield as an indication that a third number ofbits are used for both phi and psi, and processing a value of 1 in theCodebook Information subfield as an indication that a fourth number ofbits are used for both phi and psi.
 24. The access point of claim 19,wherein the sounding packet is a null data packet announcement (NDPA),wherein the NDPA includes a subfield added to a Per User Info field,wherein, when a first number of bits are to be used for both phi and psiin a case of single user (SU)-MIMO and a second number of bits are to beused for both phi and psi in a case of multiple user (MU)-MIMO, the oneor more processors execute the instructions to set the subfield to afirst value, and wherein, when a third number of bits are to be used forboth phi and psi in the case of SU-MIMO and a fourth number of bits areto be used for both phi and psi in the case of MU-MIMO, the one or moreprocessors execute the instructions to set the subfield to a secondvalue.